1. Field of the Invention
As is well known, both nitrogen and sulfur are only two of a plethora of chemical elements that are essential to proper nutrition of living plants. The plant nutrients, nitrogen and sulfur, are commonly classified by agronomists as primary and secondary, respectively, Both of these nutrients, of course, are required for most important farm crops, for example, cereals and fibers.
In 1983, the estimated annual production of by-product crystalline A/S in the United States was about 2 million short tons. The chief sources of by-product A/S are from the production of caprolactam, an intermediate in production of nylon, from production of methacrylates, and in the coking of coal. These by-products are commonly recovered as relatively dilute solutions which are subsequently concentrated to cause the A/S to precipitate in, for instance, a crystallizer unit as mainly fine crystals.
The resulting crystalline product is separated from the mother liquor, and its primary use is in the fertilizer industry. The relatively few large crystals are separated from the multiplicity of small crystals by screening and are used mainly as direct-application fertilizer or for blending with other fertilizer materials so there is a homogeneity with respect to particle sizes of the various materials.
The physical state of fine- or standard-size crystalline by-product A/S is suitable for the manufacture of chemically granulated fertilizer commonly referred to as "compound," "complex," or "cogranulated" fertilizers. In the manufacture of these types of fertilizers, all ingredients normally are mixed homogeneously prior to formation of particulate granules, with the result that each granule of the resultant fertilizer mixture contains all ingredients in the predetermined proportion and in a mechanically and/or chemically bonded, nonsegregable union. It is thusly assured that if the resulting fertilizer is applied uniformly to the soil, all ingredients therein will also be applied uniformly.
Most of the crystalline by-product A/S as recovered from the crystallizer operation supra, however, is not in suitable physical state, particularly with respect to particle size, for use in another large and important class of fertilizers generally known as "bulk-blends" or "dry-mixed" fertilizers. Fertilizers of this type consist of simple, dry, mechanial mixtures of discrete, nonbonded granules of two or more chemical compositions. The granules of different composition are blended in proportions calculated to yield a mixture of the desired overall fertilizer nutrient composition. This method of fertilizer preparation, being simple and adaptable to small production operations at or near the locations of fertilizer usage, is extremely popular in the United States. However, to ensure the homogeneity within a given small volume of such dry-blended fertilizers during mixing, handling, and field application, it has been found essential that all the various ingredients be of closely matched particle size distribution (Hoffmeister, George. "Quality Control in a Bulk Blending Plant," Proc. TVA Fertilizer Bulk Blending Conference, Louisville, Ky., Aug. 1-2, 1973). Ignoring this requirement and preparing blends from ingredients of unmatched particle size, inevitably results in segregation of the various components during mixing, handling, and field application. Thus, homogeneity will be lost and the aforementioned undesirable agronomic effect of nonhomogeneous field application will be encountered.
In view of this important requirement that individual ingredients of bulk blends be matched in particle size distribution, crystalline by-product A/S cannot be incorporated properly therein because of its small particle size.
Modern fertilizer application equipment for broadcast or for row placement application of direct-application solid fertilizer is designed for handling free-flowing granular type materials, such as granular or pelleted ammonia nitrate or urea. It absolutely will not properly handle such fine crystalline A/S. When attempts are made to apply nongranular materials such as said crystalline by-product A/S with use of conventional, modern-day application equipment, it has proved impossible to achieve uniform ground coverage becaus of ballistic action, poor flow characteristics, and bridging tendency of fine particle-size materials in the applicator.
2. Description of the Prior Art
In view of the above enumerated considerations, and since the development of the highly successful, technically viable, and economically attractive process for granulating by-product A/S, as described in the teachings of our earlier work, as is now reflected in U.S. Pat. No. 4,589,904, Harrison et al., May 20, 1986, assigned to the assignee of the present invention; substantial efforts have been directed by many practitioners in the fertilizer industry toward lowering production costs of manufacturing such granular A/S from such by-product A/S crystals. Indeed, it is expected that in the near future, industry will commercialize the process chiefly because the popularity of the granular product as an excellent source of nitrogen and water-soluble sulfur for agriculture and because the process will solve a current disposal problem for producers of the by-product A/S crystals. It also should now be obvious to those skilled in the art just how important our earlier and parent invention is to the large class of bulk-blended fertilizers. It also should now be obvious to those skilled in the art just how important the present invention is to the large class of fertilizer manufacturers whom have already recognized the worth and value of our said earlier work taken in view of the presently described work and the substantial reduction on production costs attendant thereto.